The invention relates to a process for aerobic composting and/or drying of organic waste materials in a composting bin and apparatus for carrying out the process. The bin is formed by one or, if appropriate, several composting chambers which can be aerated or vented and heated. In the case of a bin with two or more chambers, the chambers are arranged at different levels one below the other. The material is fed to the bin by dumping it in loosely, and is conveyed through the bin. After a residence time determined by the time required for composting or decomposition as a rule, this time is about ten days, the material is discharged from the bin.
These processes and this equipment are essentially used for the production of compost. Micro-organisms, such as bacteria, mold fungi, protozoa, nematodes or actinomycetes participate in the composting process, and the aerobic decomposition can be taken through to a total mineralization of the organic materials.
Decomposition or rotting depends essentially on the oxygen content, water content, C/N nutrient content, temperature and pH of the material to be converted. With a sufficient air supply, it proceeds virtually without odors, in particular, at temperatures of 60.degree. to 90.degree. on average.
In view of the increasing waste disposal problems, mixtures of garbage and effluent sludge are composted to an increasing extent.
In mixtures of these components, it is possible in some cases to set an even higher C:N ratio than the 25:1 to 30:1 ratio which is favorable for the rotting or decomposing organisms.
The tests by EAWAG in Rueschlikon confirm (compare reprint of "Neue Zuericher Zeitung", Technik supplement of June 18, 1958), the finding that sewage sludge can be added in equivalent quantities to the garbage.
Because of the increasing importance of the waste disposal problem, coupled with concern over pollution of the environment, processes which in themselves are suitable in principle, are in the end no longer usable nowadays. For example, the "Baden-Baden process" used earlier, in which open rotting pits are provided, in particular pits which are aerated by means of aeration channels, does not meet the hygienic requirements customary today.
Partial rotting has been achieved with the fermenter drum of the Dano-biostabilizer by using this as a fermenter cell.
In this drum relatively good, thorough mixing and loosening of the material does take place when air is supplied continuously. The result is a rotted or composted material which is then stored in open pits, even though for a shorter period (compare the printed publication already quoted).
The likewise known "digester evolution" relates to a virtually closed, upright standing, cylindrical fermenter cell with levels built in, the comminuted material being charged to the upper level and being mixed and conveyed through the levels by means of a vertical rotary shaft fitted with arms and colters.
The power consumption for transporting the material through the individual levels of the fermenter cell is relatively high and the equipment is very prone to wear and breakdown, so that economic considerations make it doubtful whether the compost treated in this way can be marketed widely.
The likewise known introduction of layers of material to be composted into aerated circular silos requires complicated discharge devices such as have been disclosed, for example, in German Utility Model 7,329,120.
Devices of this type are intended to enable the rotted material to be discharged uniformly over the cross-section of the vessel, and to permit ready replacement of the cutting tools or worm screws, which are subject to relatively extensive wear.
It is not easy to solve these problems and, in many cases, it is acknowledged in the result that compromises are necessary.
This situation in the end makes the principle of circular rotting silos questionable, at least as far as certain sizes and zones are concerned.
Moreover, it is known from German Offenlegungsschrift 2,890,344, to charge the material to a continuous conveyor system arranged in an aeration reactor in several levels one below the other. The dumping of the material thus obtained is only loose and essentially can initiate only drying, but not an effective biological reaction in the sense of complete decomposition or rotting since, as a rule, the air flows through the dumped layer of material on the paths of least resistance, without effectively and uniformly coming into contact with the majority of the surfaces in the material.